
const startTag = /^<([-A-Za-z0-9_]+)((?:\s+[a-zA-Z0-9_:][-a-zA-Z0-9_:.]*(?:\s*=\s*(?:(?:"[^"]*")|(?:'[^']*')|[^>\s]+))?)*)\s*(\/?)>/;
const endTag = /^<\/([-A-Za-z0-9_]+)[^>]*>/;
const attr = /([a-zA-Z0-9_:][-a-zA-Z0-9_:.]*)(?:\s*=\s*(?:(?:"((?:\\.|[^"])*)")|(?:'((?:\\.|[^'])*)')|([^>\s]+)))?/g;

function makeMap(str) {
    const obj = {};
    const items = str.split(',');
    for (let i = 0; i < items.length; i += 1) obj[items[i]] = true;
    return obj;
}

const empty = makeMap('area,base,basefont,br,col,frame,hr,img,input,link,meta,param,embed,command,keygen,source,track,wbr');

const block = makeMap('address,code,article,applet,aside,audio,blockquote,button,canvas,center,dd,del,dir,div,dl,dt,fieldset,figcaption,figure,footer,form,frameset,h1,h2,h3,h4,h5,h6,header,hgroup,hr,iframe,ins,isindex,li,map,menu,noframes,noscript,object,ol,output,p,pre,section,script,table,tbody,td,tfoot,th,thead,tr,ul,video');

const inline = makeMap('a,abbr,acronym,applet,b,basefont,bdo,big,br,button,cite,del,dfn,em,font,i,iframe,img,input,ins,kbd,label,map,object,q,s,samp,script,select,small,span,strike,strong,sub,sup,textarea,tt,u,var');

const closeSelf = makeMap('colgroup,dd,dt,li,options,p,td,tfoot,th,thead,tr');

const fillAttrs = makeMap('checked,compact,declare,defer,disabled,ismap,multiple,nohref,noresize,noshade,nowrap,readonly,selected');

function HTMLParser(html, handler) {
    let index;
    let chars;
    let match;
    let last = html;
    const stack = [];

    stack.last = () => stack[stack.length - 1];

    function parseEndTag(tag, tagName) {
        let pos;
        if (!tagName) {
            pos = 0;
        } else {
            tagName = tagName.toLowerCase();
            for (pos = stack.length - 1; pos >= 0; pos -= 1) {
                if (stack[pos] === tagName) break;
            }
        }
        if (pos >= 0) {
            for (let i = stack.length - 1; i >= pos; i -= 1) {
                if (handler.end) handler.end(stack[i]);
            }
            stack.length = pos;
        }
    }

    function parseStartTag(tag, tagName, rest, unary) {
        tagName = tagName.toLowerCase();

        if (block[tagName]) {
            while (stack.last() && inline[stack.last()]) {
                parseEndTag('', stack.last());
            }
        }

        if (closeSelf[tagName] && stack.last() === tagName) {
            parseEndTag('', tagName);
        }

        unary = empty[tagName] || !!unary;

        if (!unary) stack.push(tagName);

        if (handler.start) {
            const attrs = [];

            rest.replace(attr, function genAttr(matches, name) {
                const value = arguments[2] || arguments[3] || arguments[4] || (fillAttrs[name] ? name : '');

                attrs.push({
                    name,
                    value,
                    escaped: value.replace(/(^|[^\\])"/g, '$1\\"'), // "
                });
            });

            if (handler.start) {
                handler.start(tagName, attrs, unary);
            }
        }
    }

    while (html) {
        chars = true;

        if (html.indexOf('</') === 0) {
            match = html.match(endTag);
            if (match) {
                html = html.substring(match[0].length);
                match[0].replace(endTag, parseEndTag);
                chars = false;
            }
        } else if (html.indexOf('<') === 0) {
            match = html.match(startTag);
            if (match) {
                html = html.substring(match[0].length);
                match[0].replace(startTag, parseStartTag);
                chars = false;
            }
        }

        if (chars) {
            index = html.indexOf('<');
            let text = '';
            while (index === 0) {
                text += '<';
                html = html.substring(1);
                index = html.indexOf('<');
            }
            text += index < 0 ? html : html.substring(0, index);
            html = index < 0 ? '' : html.substring(index);

            if (handler.chars) handler.chars(text);
        }

        if (html === last) throw new Error(`Parse Error: ${html}`);
        last = html;
    }

    parseEndTag();
}

export default HTMLParser;
